

232 The Mathematical Electricians of the 



of Riemann and Weber were both abandoned in favour of a 

 third alternative. 



At the time, however, Weber's discovery was felt to be a 

 great advance ; and indeed it had, perhaps, the greatest share 

 in awakening mathematical physicists to a sense of the possi- 

 bilities latent in the theory of electricity. Beyond this, its 

 influence was felt in general dynamics ; for Weber's electro- 

 kinetic energy, which resembled kinetic energy in some respects 

 and potential energy in others, could not be precisely classified 

 under either head ; and its introduction, by helping to break 

 down the distinction which had hitherto subsisted between the 

 two parts of the kinetic potential, prepared the way for the 

 modern transformation-theory of dynamics.* 



Another subject whose development was stimulated by the 

 work of Weber was the theory of gravitation. That gravitation 

 is propagated by the action of a medium, and consequently is a 

 process requiring time for its accomplishment, had been an article 

 of faith with many generations of physicists. Indeed, the 

 dependence of the force on the distance between the attracting 

 bodies seemed to suggest this idea ; for a propagation which is 

 truly instantaneous would, perhaps, be more naturally conceived 

 to be effected by some kind of rigid connexion between the 

 bodies, which would be more likely to give a force independent 

 of the mutual distance. 



It is obvious that, if the simple law of Newton is abandoned, 

 there is a wide field of rival hypotheses from which to choose 

 its successor. The first notable attempt to discuss the question 

 was made by Laplace. f Laplace supposed gravity to be pro- 

 duced by the impulsion on the attracted body of a " gravific 

 fluid," which flows with a definite velocity toward the centre 

 of attraction say, the sun. If the attracted body or planet 

 is in motion, the velocity of the fluid relative to it will be 

 compounded of the absolute velocity of the fluid and the 

 reversed velocity of the planet, and the force of gravity will 



* Cf. "Whittaker, Analytical Dynamics, chapters ii, iii, xi. 

 t Meeanique Celeste, Livre x, chap, vii, 22. 



